Technical terminology is the specialised vocabulary of a profession or of some other activity to which a group of people dedicate significant parts of their lives (for instance, hobbies). Sometimes technical terminology is termed jargon.
Technical terminology exists in a continuum of "formality". Precise technical terms and their definitions are formally recognised, documented, and taught by educators in the field, and are similar to slang. The boundaries between formal and slang jargon, as in general English, are quite fluid, with terms sliding in and out of recognition. The relationship between formal and informal technical vocabularies is discussed in the Jargon File (which is a collection of informal jargon relating to the hacker community).
Technical terminology evolves due to the need for experts in a field to communicate with precision and brevity, and is thus unavoidable and desirable, but this often has the (usually) undesired effect of excluding those who are unfamiliar with the particular specialized language of the group. This can cause difficulties as, for example, when a patient is unable to follow the discussions of medical practitioners, and thus cannot understand their own condition and treatment. It also causes difficulties where professionals in different but related fields use different sets of specialized language and thus cannot understand each other's work - for instance, substantial amounts of duplicated research occur in cognitive psychology and human-computer interaction partly because of such difficulties. However the terms of technical terminology are used to express a great deal of information in a compact form. This makes it possible for professionals to speak to each other without having to exhaustively describe each concept; they can simply use the terms whose defintions are already known in the profession.
The term 'jargon' can, and often does, have pejorative connotations, particularly when aimed at "business culture". The marketing and public relations industries are particularly relevant here, and have made substantial contributions to the ever expanding lexicon of jargon that permeates the global business environment.
See also: Eurodicautom a free multilingual terminology database